1. Field of the Invention
The invention relates to a portable radio signal transceiver, and more particularly to prevention of disallowed use of a portable radio signal transceiver not held by an owner due to loss, theft and so on.
2. Description of the Related Art
With recent popularization of a movable communication terminal such as a portable radio signal transceiver and PHS, there is caused a problem that a movable communication terminal is not held by an owner due to loss, mislaying, theft and so on, and is illegitimately used by others.
In order to prevent such illegitimate use by others, there has bee used a movable communication terminal provided with a dial-locking function. This dial-locking function is a function by which a movable communication terminal is restricted to operate until a predetermined step, such as input of a predetermined pass-code, is carried out. Here in the specification, a word "dial-lock mode" indicates a state in which a movable communication terminal is restricted to operate by the dial-lock function, and a word "non dial-lock mode" indicates a state in which a movable communication terminal is not restricted to operate.
Hereinbelow is explained the dial-lock function in a conventional movable communication terminal.
First, there is explained a movable communication terminal having a basic dial-lock function, as first prior art. In the movable communication terminal, a pass number is stored in advance therein. The movable communication terminal is automatically transferred to a dial-lock mode when a certain operation is carried out to the movable communication terminal through a keyboard or when the movable communication terminal is turned off. When the dial-lock mode is to be cancelled, the pass number is input into the movable communication terminal through a keyboard.
Japanese Unexamined Patent Publication No. 6-216841 as second prior art has suggested a movable communication terminal which automatically transfers to a dial-lock mode when a certain period of time passes after a non dial-lock mode has started or a call has finished. The second prior art is more advantageous than the above-mentioned first prior art in that the movable communication terminal automatically transfers to a dial-lock mode even if a user does not intend to do so, ensuring enhancement in security.
Japanese Unexamined Patent Publication No. 6-125305 as third prior art has suggested a movable communication terminal which automatically responds to a call transmitted from another terminal, checks as to whether a present user is an legitimate user by virtue of a pass number having been stored in advance therein, transfers to a dial-lock mode by remote control, and displays information about a legitimate user on a display screen to thereby urge a person having the terminal in his hands to make a call to an owner.
A function by which a movable communication terminal can be dial-locked from a remote place, such as one suggested in the third prior art, is called a remote dial-lock function. The third prior art is more advantageous than the first prior art in that the movable communication terminal in the third prior art can be put into a dial-lock mode after a legitimate user has noticed that the movable communication terminal had been mislaid.
Japanese Unexamined Patent Publication No. 9-182158 as fourth prior art has suggested a portable radio signal transceiver which is capable of preventing illegitimate use thereof. In case of loss and theft, an owner of a portable radio signal transceiver registers mandatory lock data into a memory equipped in a base station through another telephone. A central processing unit in the portable radio signal transceiver reads out ID number from a memory, when a key for starting a call is actuated, and then, transmits a request for registration of location to the base station. The base station reads out the mandatory lock data out of the memory, based on the ID number, and transmits the mandatory lock data to the telephone. The telephone stores the mandatory lock data in a memory, and establishes a first flag in RAM when the mandatory lock data is indicative of disallowance in radio signal transmission, or a second flag in RAM when the mandatory lock data is indicative of allowance in radio signal transmission. When the first flag is established, data about operation having been input through keys is made invalid, whereas when the second flag is established, data about operation having been input through keys is made valid.
However, the above-mentioned first to fourth prior art are accompanied with problems as follows.
The first prior art is accompanied with a problem that it is impossible to transfer the movable communication terminal into a dial-lock mode, if a user actually has the movable communication terminal in his hands. In other words, it would be impossible to prevent illegitimate use, if the movable communication terminal is set in a dial-lock mode when the movable communication terminal is away from a user.
This problem may be solved, if the movable communication terminal is always set in a dial-lock mode when a legitimate user does not use the movable communication terminal. However, this solution is accompanied with another problem that it will be necessary to set or cancel a dial-lock mode each time the movable communication terminal is used, which deteriorates serviceability of the movable communication terminal.
In accordance with the second prior art, it would not be necessary for a legitimate user to have a habit of setting the movable communication terminal into a dial-lock mode after using the movable communication terminal, since the movable communication terminal is automatically transferred into a dial-lock mode, if a certain period of time has passed. However, since the movable communication terminal is put in a dial-lock mode if a certain period of time has passed, a user has to cancel a dial-lock mode each time a user uses the movable communication terminal, unless a user successively uses the movable communication terminal.
In accordance with the third prior art, it is possible to set the movable communication terminal into a dial-lock mode by remote control even after a legitimate user has noticed loss of the movable communication terminal. However, since the movable communication terminal in the third prior art checks as to whether a present user is a legitimate user or not after making a response to a call, it is unavoidable for the movable communication terminal to automatically make a response to a unconcerned call from others.
The portable radio signal transceiver in accordance with the fourth prior art is accompanied with a problem that it is necessary for a legitimate user to use another telephone in order to dial-lock the portable radio signal transceiver.